Predictive value of known and novel alleles of CYP2B6 for efavirenz plasma concentrations in HIV-infected individuals

Drug-drug interaction profile of ritlecitinib as perpetrator and victim through cytochrome P450

AIMS

To assess the effect of a potent cytochrome P450 (CYP) 3A inhibitor and CYP inducer on the pharmacokinetics of ritlecitinib, a JAK3/TEC family kinase inhibitor, and assess the effect of ritlecitinib on the pharmacokinetics of CYP substrates (midazolam, efavirenz, tolbutamide, caffeine and oral contraceptives [ethinyl oestradiol and levonorgestrel]) in healthy adults.

METHODS

Seven clinical drug-drug interaction studies were analysed. Pharmacokinetic parameters for drugs as measured in blood plasma were used to estimate the drug interaction potential with ritlecitinib as a perpetrator or victim.

RESULTS

Midazolam exposure (area under plasma concentration-time curve from time 0 to infinity [AUCinf]) and peak exposure (maximum concentration [Cmax]) were increased by ≈169% and ≈80.1%, respectively, in the presence of ritlecitinib. Efavirenz exposure (AUC0-72) and peak exposure (Cmax) were similar in the presence and absence of ritlecitinib coadministration. Tolbutamide pharmacokinetic parameters (AUCinf and Cmax) were not affected by multiple ritlecitinib doses. In the presence of ritlecitinib, AUCinf and Cmax of caffeine increased by ≈165% and ≈10%, respectively. AUCinf and Cmax of ethinyl oestradiol decreased by ≈18% and ≈12%, respectively, following coadministration of multiple ritlecitinib 200 mg once-daily doses, but no relevant change was observed following multiple 50 mg once-daily doses. Ritlecitinib doses did not affect the pharmacokinetics of levonorgestrel. Coadministration following multiple itraconazole doses increased ritlecitinib AUCinf by ≈15%. Coadministration following multiple rifampicin doses decreased AUCinf of ritlecitinib by ≈45%.

CONCLUSIONS

Ritlecitinib is a moderate inhibitor of CYP3A and CYP1A2. Strong CYP inducers can reduce ritlecitinib concentrations, but not to clinically relevant levels leading to lack of benefit.

Activity Variations of CYP2B6 Determine the Metabolic Stratification of Efavirenz

PURPOSE

To investigate the effects of hepatic enzyme activity variations and CYP2B6 gene polymorphisms on the in vivo and in vitro metabolism of efavirenz.

MAIN METHODS

In vitro enzyme systems using rat and human liver microsomes (RLM/HLM) were established, with in vivo studies conducted on Sprague-Dawley rats. Metabolite detection was performed via LC-MS/MS. Human recombinant CYP2B6 microsomes were prepared using a baculovirus-insect cell system and ultracentrifugation, with efavirenz serving as the substrate to study enzyme kinetics.

RESULTS

Isavuconazole exhibited an IC50 of 21.14 ± 0.57 μM in RLM, indicating a mixed competitive and noncompetitive mechanism, and an IC50 of 40.44 ± 4.23 μM in HLM, suggesting an anticompetitive mechanism. In rats, coadministration of efavirenz and isavuconazole significantly increased the AUC, Tmax, and Cmax of efavirenz. Co-administration of efavirenz and rifampicin significantly elevated the AUC, Tmax, and Cmax of 8-OH-efavirenz. The activity of CYP2B6.4, 6, and 7 increased significantly compared to CYP2B6.1, with relative clearance ranging from 158.34% to 212.72%. Conversely, the activity of CYP2B6.3, 8, 10, 11, 13-15, 18-21, 23-27, 31-33, and 37 was markedly reduced, ranging from 4.30% to 79.89%.

CONCLUSION

Variations in liver enzyme activity and CYP2B6 genetic polymorphisms can significantly alter the metabolism of efavirenz. It provides laboratory-based data for the precise application of efavirenz and other CYP2B6 substrate drugs.

Challenges and Opportunities for Consideration of Efavirenz Drug Repurposing for Alzheimer's Disease Therapeutics

Therapeutic research and development for Alzheimer's disease (AD) has been an area of intense research to alleviate memory loss and neurodegeneration. There is growing interest in drug repositioning and repurposing strategies for FDA-approved medications as potential candidates that may further advance AD therapeutics. The FDA drug efavirenz has been investigated as a candidate drug for repurposing as an AD medication. The proposed mechanism of action of efavirenz (at low doses) is the activation of the neuron-specific enzyme CYP46A1 that converts excess brain cholesterol into 24-hydroxycholesterol (24-HC) that is exported to the periphery. Efavirenz at a low dose was found to improve memory deficit in the 5XFAD model of AD that was accompanied by elevated 24-HC and reduction in Aβ; furthermore, efavirenz reduced pTau and excess cholesterol levels in human iPSC-derived Alzheimer's neurons. The low dose of efavirenz used in the AD mouse model to increase 24-HC contrasts with the use of more than 100-fold higher doses of efavirenz for clinical treatment of human immunodeficiency virus (HIV) through inhibition of reverse transcriptase. Low doses of efavirenz may avoid neurotoxic adverse effects that occur at high efavirenz doses used for HIV treatment. This review evaluates the drug properties of efavirenz with respect to its preclinical data on regulating memory deficit, pharmacokinetics, pharmacodynamics, metabolites, and genetic variabilities in drug metabolism as well as its potential adverse effects. These analyses discuss the challenges and questions that should be addressed in future studies to consider the opportunity for low dose efavirenz as a candidate for AD drug development.

Genetic variants, haplotype determination, and function of novel alleles of CYP2B6 in a Han Chinese population

Amino acid variants in protein may result in deleterious effects on enzymatic activity. In this study we investigate the DNA variants on activity of CYP2B6 gene in a Chinese Han population for potential use in precision medicine. All exons in CYP2B6 gene from 1483 Chinese Han adults (Zhejiang province) were sequenced using Sanger sequencing. The effects of nonsynonymous variants on recombinant protein catalytic activity were investigated in vitro with Sf12 system. The haplotype of novel nonsynonymous variants with other single nucleotide variants in the same allele was determined using Nanopore sequencing. Of 38 alleles listed on the Pharmacogene Variation Consortium, we detected 7 previously reported alleles and 18 novel variants, of which 11 nonsynonymous variants showed lower catalytic activity (0.00-0.60) on bupropion compared to CYP2B6*1. Further, these 11 novel star-alleles (CYP2B6*39-49) were assigned by the Pharmacogene Variation Consortium, which may be valuable for pharmacogenetic research and personalized medicine.

Pharmacogenetics of weight gain following switch from efavirenz- to integrase inhibitor-containing regimens

BACKGROUND

Excessive weight gain affects some persons with HIV after switching to integrase strand transfer inhibitor (INSTI)-containing antiretroviral therapy (ART). We studied associations between CYP2B6 genotype and weight gain after ART switch among ACTG A5001 and A5322 participants.

METHODS

Eligible participants switched from efavirenz- to INSTI-containing ART, had genotype data, and had weight data at least once from 4 weeks to 2 years post-switch. Multivariable linear mixed effects models adjusted for race/ethnicity, CD4, age, BMI and INSTI type assessed relationships between CYP2B6 genotype and estimated differences in weight change.

RESULTS

A total of 159 eligible participants switched ART from 2007 to 2019, of whom 138 had plasma HIV-1 RNA < 200 copies/mL (65 CYP2B6 normal, 56 intermediate, 17 poor metabolizers). Among participants with switch HIV-1 RNA < 200 copies/mL, weight increased in all 3 CYP2B6 groups. The rate of weight gain was greater in CYP2B6 poor than in CYP2B6 normal metabolizers overall, and within 9 subgroups (male, female, White, Black, Hispanic, dolutegravir, elvitegravir, raltegravir, and TDF in the pre-switch regimen); only in Hispanic and elvitegravir subgroups were these associations statistically significant ( P  < 0.05). Compared to normal metabolizers, CYP2B6 intermediate status was not consistently associated with weight gain.

CONCLUSION

CYP2B6 poor metabolizer genotype was associated with greater weight gain after switch from efavirenz- to INSTI-containing ART, but results were inconsistent. Weight gain in this setting is likely complex and multifactorial.

Role of Cytochrome P450 3A4 in Cancer Drug Resistance: Challenges and Opportunities

One of the biggest obstacles to the treatment of diseases, particularly serious conditions like cancer, is therapeutic resistance. The process of drug resistance is influenced by a number of important variables, including MDR genes, drug efflux, low-quality medications, inadequate dosage, etc. Drug resistance must be addressed, and new combinations based on the pharmacokinetics/pharmacodynamics (PK-PD) characteristics of the partner pharmaceuticals must be developed in order to extend the half-lives of already available medications. The primary mechanism of drug elimination is hepatic biotransformation of medicines by cytochrome P450 (CYP) enzymes; of these CYPs, CYP3A4 makes up 30-40% of all known cytochromes that metabolize medications. Induction or inhibition of CYP3A4-mediated metabolism affects the pharmacokinetics of most anticancer drugs, but these details are not fully understood and highlighted because of the complexity of tumor microenvironments and various influencing patient related factors. The involvement of CYPs, particularly CYP3A4 and other drug-metabolizing enzymes, in cancer medication resistance will be covered in the current review.

Pharmacogenomics and adverse effects of anti-infective drugs in children

Children, as a special group, have their own peculiarities in terms of individualized medication use compared to adults. Adverse drug reactions have been an important issue that needs to be addressed in the hope of safe medication use in children, and the occurrence of adverse drug reactions is partly due to genetic factors. Anti-infective drugs are widely used in children, and they have always been an important cause of the occurrence of adverse reactions in children. Pharmacogenomic technologies are becoming increasingly sophisticated, and there are now many guidelines describing the pharmacogenomics of anti-infective drugs. However, data from paediatric-based studies are scarce. This review provides a systematic review of the pharmacogenomics of anti-infective drugs recommended for gene-guided use in CPIC guidelines by exploring the relationship between pharmacogenetic frequencies and the incidence of adverse reactions, which will help inform future studies of individualized medication use in children.

Mechanistic Modeling of the Drug-Drug Interaction Between Efavirenz and Dolutegravir: Is This Interaction Clinically Relevant When Switching From Efavirenz to Dolutegravir During Pregnancy?

Following the 2021 World Health Organization's updated recommendations on the management of HIV infection, millions of people living with HIV are currently switched from efavirenz-based antiretroviral therapy to dolutegravir-based antiretroviral therapy. Pregnant individuals transitioning from efavirenz to dolutegravir might be at increased risk of insufficient viral suppression in the immediate postswitch period because both efavirenz- and pregnancy-related increases in hormone levels induce enzymes involved in dolutegravir metabolism, namely, cytochrome P450 3A4 and uridine 5'-diphospho-glucuronosyltransferase 1A1. This study aimed at developing physiologically based pharmacokinetic models to simulate the switch from efavirenz to dolutegravir in the late second and third trimester. To this end, the drug-drug interaction between efavirenz and the uridine 5'-diphospho-glucuronosyltransferase 1A1 substrates dolutegravir and raltegravir was first simulated in nonpregnant subjects. After successful validation, the physiologically based pharmacokinetic models were translated to pregnancy and dolutegravir pharmacokinetics following efavirenz discontinuation were predicted. Modeling results indicated that, at the end of the second trimester, both efavirenz concentrations and dolutegravir trough concentrations fell below respective pharmacokinetic target thresholds (defined as reported thresholds producing 90%-95% of the maximum effect) during the time interval from 9.75 to 11 days after dolutegravir initiation. At the end of the third trimester, this time interval spanned from 10.3 days to >4 weeks after dolutegravir initiation. These findings suggest that dolutegravir exposure in the immediate post-efavirenz switch period during pregnancy may be suboptimal, leading to HIV viremia and, potentially, resistance. The clinical implications of these findings remain to be substantiated by future studies.

Efavirenz: History, Development and Future

Efavirenz (Sustiva^®) is a first-generation non-nucleoside reverse transcriptase inhibitor (NNRTI) used to treat human immunodeficiency virus (HIV) type 1 infection or to prevent the spread of HIV. In 1998, the FDA authorized efavirenz for the treatment of HIV-1 infection. Patients formerly required three 200 mg efavirenz capsules daily, which was rapidly updated to a 600 mg tablet that only required one tablet per day. However, when given 600 mg once daily, plasma efavirenz concentrations were linked not only to poor HIV suppression but also to toxicity. Clinical data suggested that the standard dose of efavirenz could be reduced without compromising its effectiveness, resulting in a reduction in side effects and making the drug more affordable. Therefore, ENCORE1 was performed to compare the efficiency and safeness of a reduced dose of efavirenz (400 mg) with the standard dose (600 mg) plus two NRTI in antiretroviral-naïve HIV-infected individuals. Nowadays, due to the emergence of integrase strand transfer inhibitors (INSTIs), some consider that it is time to stop using efavirenz as a first-line treatment on a global scale, in the parts of the world where that is possible. Efavirenz has been a primary first-line antiviral drug for more than 15 years. However, at this moment, the best use for efavirenz could be for pre-exposure prophylaxis (PrEP) and repurposing in medicine.

Influence of CYP2B6 and CYP3A4 polymorphisms on the virologic and immunologic responses of patients treated with efavirenz-containing regimen

OBJECTIVES

The main objective of this study was to evaluate the effect of CYP2B6 and CYP3A4 polymorphisms on the virological and immunologic responses of HIV patients. A total of 153 HIV-positive patients were enlisted for the study.

PATIENTS AND METHODS

Viral load and median CD4 T cell counts were evaluated at baseline and month 6 (M6). Samples were identified using TaqMan genotyping assays.

RESULTS

The AG in CYP2B6 rs2279343 was associated with VLS compared to homozygous AA. In the dominant model, the AG/GG genotypes were associated with VLS compared to the AA genotype. Moreover, in overdominant model, the AG genotype was associated with VLS compared to AA/GG. Regarding immunological response, only the AG in SNP rs2279343 CYP2B6 was associated with an increase in CD4 cell count between baseline and M6. In CYP2B6 rs3745274, the CD4 cell count at M6 was higher than that of baseline for GG carriers and for GT carriers. In CYP3A4 rs2740574, the TC carriers showed a higher median CD4 count at M6 compared to that of the baseline count, as well as for CC carriers. The best genotypes combination associated with CD4 cell count improvement were AA/AG in SNP rs2279343 and GG/GT in SNP rs3745274.

CONCLUSION

Our findings support the fact that CYP2B6 rs2279343 could help in the prediction of VLS and both SNPs rs3745274 and rs2279343 in CYP2B6 and CYP3A4 rs2740574 were associated with immune recovery in Malian HIV-positive patients.

Quantitative Prediction of Drug Interactions Caused by Cytochrome P450 2B6 Inhibition or Induction

BACKGROUND

Numerous drugs have the potential to be affected by cytochrome P450 (CYP) 2B6-mediated drug-drug interactions (DDIs).

OBJECTIVES

In this work, we extend a static approach to the prediction of the extent of pharmacokinetics DDIs between substrates and inhibitors or inducers of CYP2B6.

METHODS

This approach is based on the calculation of two parameters (the contribution ratio [CR], representing the fraction of dose of the substrate metabolized via this pathway and the inhibitory or inducing potency of the perpetrator [IR or IC, respectively]) calculated from the area under the concentration-time curve (AUC) ratios obtained in in-vivo DDI studies.

RESULTS

Forty-eight studies involving 5 substrates, 11 inhibitors and 18 inducers of CYP2B6 (overall 15 inhibition and 33 induction studies) were divided into test and validation sets and considered for estimation of the parameters. The proposed approach demonstrated a fair accuracy for predicting the extent of DDI related to CYP2B6 inhibition and induction, all predictions related to the validation test (N = 18) being 50-200% of the observed ratios.

CONCLUSIONS

This methodology can be used for proposing initial dose adaptations to be adopted, for example in clinical use or for designing DDI studies involving this enzyme.

CYP2B6 allelic variants and non-genetic factors influence CYP2B6 enzyme function

Human CYP2B6 enzyme although constitutes relatively low proportion (1–4%) of hepatic cytochrome P450 content, it is the major catalyst of metabolism of several clinically important drugs (efavirenz, cyclophosphamide, bupropion, methadone). High interindividual variability in CYP2B6 function, contributing to impaired drug-response and/or adverse reactions, is partly elucidated by genetic polymorphisms, whereas non-genetic factors can significantly modify the CYP2B6 phenotype. The influence of genetic and phenoconverting non-genetic factors on CYP2B6-selective activity and CYP2B6 expression was investigated in liver tissues from Caucasian subjects (N = 119). Strong association was observed between hepatic S-mephenytoin N-demethylase activity and CYP2B6 mRNA expression (P < 0.0001). In less than one third of the tissue donors, the CYP2B6 phenotype characterized by S-mephenytoin N-demethylase activity and/or CYP2B6 expression was concordant with CYP2B6 genotype, whereas in more than 35% of the subjects, an altered CYP2B6 phenotype was attributed to phenoconverting non-genetic factors (to CYP2B6-specific inhibitors and inducers, non-specific amoxicillin + clavulanic acid treatment and chronic alcohol consumption, but not to the gender). Furthermore, CYP2B6 genotype–phenotype mismatch still existed in one third of tissue donors. In conclusion, identifying potential sources of CYP2B6 variability and considering both genetic variations and non-genetic factors is a pressing requirement for appropriate elucidation of CYP2B6 genotype–phenotype mismatch.

Frequencies of CYP2B6∗4,∗5, and ∗6 Alleles within an Iranian Population (Mazandaran)

Background

The human CYP2B subfamily consists of one functional gene (CYP2B6) and one pseudogene (CYP2B7P). Cytochrome P450 2B6 (CYP2B6) is a highly polymorphic enzyme that shows marked interindividual and interethnic variations. Currently, 38 alleles have been described, and some of the allelic variants have been associated with low enzyme activity. The aim of this study was to investigate the frequencies of CYP2B6^∗4, CYP2B6^∗5, and CYP2B6^∗6 alleles in the Mazani ethnic group among Iranian Population.

Methods

The study was conducted in 289 unrelated healthy volunteers. DNA was extracted from peripheral blood and analyzed by the PCR-RFLP protocol. The PCR product was digested with restriction enzymes and then separated using agarose gel electrophoresis.

Results

The frequency of CYP2B6^∗4, CYP2B6^∗5, and CYP2B6^∗6 in this study was 34.60%, 7.26%, and 34.54%, respectively.

Conclusion

The frequency of the CYP2B6^∗4 allele in the Mazani ethnic group was much higher (34.60%) than other population. The frequency of CYP2B6^∗6 (34.54%) also was higher than its frequency in other previously reported population. But the frequency of CYP2B6^∗5 in this study was lower than expected. These results will be useful in understanding the ethnic diversity in Iranian population and offer a preliminary basis for more rational use of drugs that are substrates for CYP2B6 in this population.

Pregnancy Has No Clinically Significant Effect on the Pharmacokinetics of Bupropion or Its Metabolites

BACKGROUND

Bupropion (BUP) is a chiral antidepressant and smoking cessation aide with benefits and side effects correlated with parent and active metabolite concentrations. BUP is metabolized by CYP2B6, CYP2C19, and CYP3A4 to hydroxy-BUP (OH-BUP) as well as by 11β-hydroxysteroid dehydrogenase-1 and aldo-keto reductases to threohydrobupropion (Threo) and erythrohydrobupropion (Erythro), respectively. As pregnancy alters the activity of drug-metabolizing enzymes, the authors hypothesized that BUP metabolism and BUP metabolite concentrations would be altered during pregnancy, potentially affecting the efficacy and safety of BUP in pregnant women.

METHODS

Pregnant women (n = 8) taking BUP chronically were enrolled, and steady-state plasma samples and dosing interval urine samples were collected during pregnancy and postpartum. Maternal and umbilical cord venous blood samples were collected at delivery from 3 subjects, and cord blood/maternal plasma concentration ratios were calculated. The concentrations of BUP stereoisomers and their metabolites were measured. Paired t tests were used to compare pharmacokinetic parameters during pregnancy and postpartum.

RESULTS

No significant changes were observed in the steady-state plasma concentrations, metabolite to parent ratios, formation clearances, or renal clearance of any of the compounds during pregnancy when compared with postpartum. The umbilical cord venous plasma concentrations of BUP and its metabolites were 30%-60% lower than maternal plasma concentrations.

CONCLUSIONS

This study showed that there are no clinically meaningful differences in the stereoselective disposition of BUP or its metabolites during pregnancy, indicating that dose adjustment during pregnancy may not be necessary. The results also showed that the placenta provides a partial barrier for bupropion and its metabolite distribution to the fetus, with possible placental efflux transport of bupropion and its metabolites.

Efavirenz Pharmacogenetics and Weight Gain Following Switch to Integrase Inhibitor-Containing Regimens

BACKGROUND

Unwanted weight gain affects some people living with human immunodeficiency virus (HIV) who are prescribed integrase strand transfer inhibitors (INSTIs). Mechanisms and risk factors are incompletely understood.

METHODS

We utilized 2 cohorts to study pharmacogenetics of weight gain following switch from efavirenz- to INSTI-based regimens. In an observational cohort, we studied weight gain at 48 weeks following switch from efavirenz- to INSTI-based regimens among patients who had been virologically suppressed for at least 2 years at a clinic in the United States. Associations were characterized with CYP2B6 and UGT1A1 genotypes that affect efavirenz and INSTI metabolism, respectively. In a clinical trials cohort, we studied weight gain at 48 weeks among treatment-naive participants who were randomized to receive efavirenz-containing regimens in AIDS Clinical Trials Group studies A5095, A5142, and A5202 and did not receive INSTIs.

RESULTS

In the observational cohort (n = 61), CYP2B6 slow metabolizers had greater weight gain after switch (P = .01). This was seen following switch to elvitegravir or raltegravir, but not dolutegravir. UGT1A1 genotype was not associated with weight gain. In the clinical trials cohort (n = 462), CYP2B6 slow metabolizers had lesser weight gain at week 48 among participants receiving efavirenz with tenofovir disoproxil fumarate (P = .001), but not those receiving efavirenz with abacavir (P = .65). Findings were consistent when stratified by race/ethnicity and by sex.

CONCLUSIONS

Among patients who switched from efavirenz- to INSTI-based therapy, CYP2B6 genotype was associated with weight gain, possibly reflecting withdrawal of the inhibitory effect of higher efavirenz concentrations on weight gain. The difference by concomitant nucleoside analogue is unexplained.

PharmVar GeneFocus: CYP2B6

The Pharmacogene Variation Consortium (PharmVar) catalogs star (*) allele nomenclature for the polymorphic human CYP2B6 gene. Genetic variation within the CYP2B6 gene locus impacts the metabolism or bioactivation of clinically important drugs. Of particular importance are efficacy and safety concerns regarding: efavirenz, which is used for the treatment of HIV type-1 infection; methadone, a mainstay in the treatment of opioid use disorder and as an analgesic; ketamine, used as an antidepressant and analgesic; and bupropion, which is prescribed to treat depression and for smoking cessation. This GeneFocus provides a comprehensive overview and summary of CYP2B6 and describes how haplotype information catalogued by PharmVar is utilized by the Pharmacogenomics Knowledgebase (PharmGKB) and the Clinical Pharmacogenetics Implementation Consortium (CPIC).

HIV-1 and human genetic variation

Over the past four decades, research on the natural history of HIV infection has described how HIV wreaks havoc on human immunity and causes AIDS. HIV host genomic research, which aims to understand how human genetic variation affects our response to HIV infection, has progressed from early candidate gene studies to recent multi-omic efforts, benefiting from spectacular advances in sequencing technology and data science. In addition to invading cells and co-opting the host machinery for replication, HIV also stably integrates into our own genome. The study of the complex interactions between the human and retroviral genomes has improved our understanding of pathogenic mechanisms and suggested novel preventive and therapeutic approaches against HIV infection.

How Can Drug Metabolism and Transporter Genetics Inform Psychotropic Prescribing?

Many genetic variants in drug metabolizing enzymes and transporters have been shown to be relevant for treating psychiatric disorders. Associations are strong enough to feature on drug labels and for prescribing guidelines based on such data. A range of commercial tests are available; however, there is variability in included genetic variants, methodology, and interpretation. We herein provide relevant background for understanding clinical associations with specific variants, other factors that are relevant to consider when interpreting such data (such as age, gender, drug-drug interactions), and summarize the data relevant to clinical utility of pharmacogenetic testing in psychiatry and the available prescribing guidelines. We also highlight areas for future research focus in this field.

Meta-analysis of the effect of CYP2B6, CYP2A6, UGT2B7 and CAR polymorphisms on efavirenz plasma concentrations

BACKGROUND

Efavirenz primary metabolism is catalysed by CYP2B6 with minor involvement of CYP2A6. Subsequently, phase I metabolites are conjugated by UGT2B7, and constitutive androstane receptor (CAR) has been shown to transcriptionally regulate many relevant enzymes and transporters. Several polymorphisms occurring in the genes coding for these proteins have been shown to impact efavirenz pharmacokinetics in some but not all studies.

OBJECTIVES

A meta-analysis was performed to assess the overall effect of CYP2B6 rs3745274, CYP2A6 (rs28399454, rs8192726 and rs28399433), UGT2B7 (rs28365062 and rs7439366) and NR1I3 (rs2307424 and rs3003596) polymorphisms on mid-dose efavirenz plasma concentrations.

METHODS

Following a literature review, pharmacokinetic parameters were compiled and a meta-analysis for these variants was performed using Review Manager and OpenMetaAnalyst. A total of 28 studies were included.

RESULTS

Unsurprisingly, the analysis confirmed that individuals homozygous for the T allele for CYP2B6 rs3745274 had significantly higher efavirenz concentrations than those homozygous for the G allele [weighted standard mean difference (WSMD) = 2.98; 95% CI 2.19-3.76; P < 0.00001]. A subgroup analysis confirmed ethnic differences in frequency but with a similar effect size in each ethnic group (P = 0.96). Associations with CYP2A6 and UGT2B7 variants were not statistically significant, but T homozygosity for CAR rs2307424 was associated with significantly lower efavirenz concentrations than in C homozygotes (WSMD = -0.32; 95% CI -0.59 to -0.06; P = 0.02).

CONCLUSIONS

This meta-analysis provides the overall effect size for the impact of CYP2B6 rs3745274 and NR1I3 rs2307424 on efavirenz pharmacokinetics. The analysis also indicates that some previous associations were not significant when interrogated across studies.

Analysis of protein missense alterations by combining sequence- and structure-based methods

BACKGROUND

Different types of in silico approaches can be used to predict the phenotypic consequence of missense variants. Such algorithms are often categorized as sequence based or structure based, when they necessitate 3D structural information. In addition, many other in silico tools, not dedicated to the analysis of variants, can be used to gain additional insights about the possible mechanisms at play.

METHODS

Here we applied different computational approaches to a set of 20 known missense variants present on different proteins (CYP, complement factor B, antithrombin and blood coagulation factor VIII). The tools that were used include fast computational approaches and web servers such as PolyPhen-2, PopMusic, DUET, MaestroWeb, SAAFEC, Missense3D, VarSite, FlexPred, PredyFlexy, Clustal Omega, meta-PPISP, FTMap, ClusPro, pyDock, PPM, RING, Cytoscape, and ChannelsDB.

RESULTS

We observe some conflicting results among the methods but, most of the time, the combination of several engines helped to clarify the potential impacts of the amino acid substitutions.

CONCLUSION

Combining different computational approaches including some that were not developed to investigate missense variants help to predict the possible impact of the amino acid substitutions. Yet, when the modified residues are involved in a salt-bridge, the tools tend to fail, even when the analysis is performed in 3D. Thus, interactive structural analysis with molecular graphics packages such as Chimera or PyMol or others are still needed to clarify automatic prediction.

The far-reaching HAND of cART: cART effects on astrocytes

Following the introduction of combination antiretroviral therapy (cART), the morbidity and mortality from human immunodeficiency virus (HIV) infection has been drastically curtailed and HIV has now become a chronic manageable disease. Persons living with HIV (PLWH) are living longer and experiencing significant co-morbidities and conditions of aging. NeuroHIV, clinically defined as HIV-Associated Neurocognitive Disorders (HAND) and pathologically manifested by persistent inflammation in the CNS despite cART, is a significant co-morbid condition for PLWH. In the pre-cART era, HIV mediated much of the pathogenesis in the Central Nervous System (CNS); in the cART era, with low to undetectable viremia, other mechanisms may be contributing to persistent neuroinflammation. Emerging data point to the adverse effects at the cellular level of cART, independent of HIV. Astrocytes are the most abundant cells in the CNS, playing vital roles in maintaining CNS homeostasis (e.g. metabolic support to neurons, clearance of neurotransmitters, ion balance, modulation of synaptic functions and maintaining the structural integrity of the blood brain barrier (BBB). Therefore, any disruption of their function will have wide repercussions in the CNS. In this review, we will address current knowledge and gaps on the impact of antiretrovirals (ARVs) on astrocytes and physiologic consequences in the CNS. Understanding the status of this field, will provide a practical framework to elucidate the potential role of cART-mediated dysregulation of astrocytes in neuroHIV pathogenesis and inform therapeutic strategies that are "neuro-friendly". Graphical abstract CNS-penetrating cART have the potential to cause resting astrocytes to become activated into an A1 or neurotoxic phenotype. These cells can in turn secrete inflammatory cytokines that affect surrounding microglia macrophages, as well as neurotoxic factors that impact nearby neurons. In addition, impairment in the physiologic functions of astrocytes will result in altered BBB permeability and disrupted metabolic homeostasis. CNS=Central Nervous System; cART=combined antiretroviral therapy; BBB=blood brain barrier.

CYP2B6 Genotype-Dependent Inhibition of CYP1A2 and Induction of CYP2A6 by the Antiretroviral Drug Efavirenz in Healthy Volunteers

We investigated the effect of efavirenz on the activities of cytochrome P450 (CYP)1A2, CYP2A6, xanthine oxidase (XO), and N-acetyltransferase 2 (NAT2), using caffeine as a probe. A single 150 mg oral dose of caffeine was administered to healthy volunteers (n = 58) on two separate occasions; with a single 600 mg oral dose of efavirenz and after treatment with 600 mg/day efavirenz for 17 days. Caffeine and its metabolites in plasma and urine were quantified using liquid chromatography/tandem-mass spectrometry. DNA was genotyped for CYP2B6*4 (785A>G), CYP2B6*9 (516G>T), and CYP2B6*18 (983T>C) alleles using TaqMan assays. Relative to single-dose efavirenz treatment, multiple doses of efavirenz decreased CYP1A2 (by 38%) and increased CYP2A6 (by 85%) activities (P < 0.05); XO and NAT2 activities were unaffected. CYP2B6*6*6 genotype was associated with lower CYP1A2 activity following both single and multiple doses of efavirenz. No similar association was noted for CYP2A6 activity. This is the first report showing that efavirenz reduces hepatic CYP1A2 and suggesting chronic efavirenz exposure likely enhances the elimination of CYP2A6 substrates. This is also the first to report the extent of efavirenz-CYP1A2 interaction may be efavirenz exposure-dependent and CYP2B6 genotype-dependent.

Clinical Pharmacogenetics Implementation Consortium (CPIC) Guideline for CYP2B6 and Efavirenz-Containing Antiretroviral Therapy

The HIV type-1 nonnucleoside reverse transcriptase inhibitor, efavirenz, is widely used to treat HIV type-1 infection. Efavirenz is predominantly metabolized into inactive metabolites by cytochrome P450 (CYP)2B6, and patients with certain CYP2B6 genetic variants may be at increased risk for adverse effects, particularly central nervous system toxicity and treatment discontinuation. We summarize the evidence from the literature and provide therapeutic recommendations for efavirenz prescribing based on CYP2B6 genotypes.

Methadone dosing strategies in preterm neonates can be simplified

AIMS

A dramatic increase in newborn infants with neonatal abstinence syndrome has been observed and these neonates are frequently treated with complex methadone dosing schemes to control their withdrawal symptoms. Despite its abundant use, hardly any data on the pharmacokinetics (PK) of methadone is available in preterm neonates. Therefore we investigated developmental PK of methadone and evaluated current dosing strategies and possible simplification in this vulnerable population.

METHODS

A single-centre open-label prospective study was performed to collect PK data after a single oral dose of methadone in preterm neonates. A population PK model was built to characterize developmental PK of (R)- and (S)-methadone. Model-based simulations were performed to identify a simplified dosing strategy to reach and maintain target methadone exposure.

RESULTS

A total of 121 methadone concentrations were collected from 31 preterm neonates. A one-compartment model with first order absorption and elimination kinetics best described PK data for (R)- and (S)-methadone. Clearance increases with advancing gestational age and differs between R- and S-enantiomer, being slightly higher for the former (0.244 vs 0.167 L/h). Preterm neonates reached target exposure after 48 hours with currently used dosing schedules. Output from simulations revealed that target exposures can be achieved with a simplified dosing strategy during the first 4 days of treatment.

CONCLUSION

Methadone clearance in preterm neonates increases with advancing gestational age and its disposition is influenced by its chirality. Simulations that account for developmental PK changes indicate a shorter methadone dosing strategy can maintain target exposure to control withdrawal symptoms.

Physiologically based pharmacokinetic modelling prediction of the effects of dose adjustment in drug-drug interactions between levonorgestrel contraceptive implants and efavirenz-based ART

Background

HIV-positive women receiving efavirenz-based ART and levonorgestrel contraceptive implants are at risk of low levonorgestrel exposure and unintended pregnancy.

Objectives

To investigate clinically applicable dose-adjustment strategies to overcome the known drug-drug interaction (DDI) between levonorgestrel and efavirenz, using a physiologically based pharmacokinetic (PBPK) modelling-based approach.

Methods

A PBPK model was qualified against clinical data to predict levonorgestrel plasma concentrations when standard-dose (150 mg) levonorgestrel implants were administered alone (control group), as well as when standard-dose or increased-dose (300 mg) levonorgestrel implants were coadministered with either 600 or 400 mg of efavirenz.

Results

No difference was seen between in vivo clinical and PBPK-model-simulated levonorgestrel plasma concentrations (P > 0.05). Simulated levonorgestrel plasma concentrations were ∼50% lower at 48 weeks post-implant-placement in virtual individuals receiving standard-dose levonorgestrel with either 600 or 400 mg of efavirenz compared with the control group (efavirenz:control geometric mean ratio = 0.42 and 0.49, respectively). Conversely, increased-dose levonorgestrel in combination with either 600 or 400 mg of efavirenz was sufficient to restore levonorgestrel concentrations to levels similar to those observed in the 150 mg levonorgestrel control group 48 weeks post-implant-placement (efavirenz:control geometric mean ratio = 0.86 and 1.03, respectively).

Conclusions

These results suggest that the clinically significant DDI between efavirenz and levonorgestrel is likely to persist despite efavirenz dose reduction, whereas dose escalation of implantable levonorgestrel may represent a successful clinical strategy to circumvent efavirenz-levonorgestrel DDIs and will be of use to inform clinical trial design to assess coadministration of efavirenz and levonorgestrel implants.

Occurrence of CYP2B6 516G>T polymorphism in patients with ARV-associated hepatotoxicity

Background

Hepatic enzyme cytochrome P450 2B6 (CYP2B6) plays a role in the metabolism of efavirenz drugs. CYP2B6 516G>T variation showed an implication for HIV treatment.

Methods

CYP2B6 516G>T polymorphism was genotyped in a total 165 HIV patients that include 34 with and 131 without hepatotoxicity and 155 healthy individuals by the PCR‐RFLP.

Results

In patients with hepatotoxicity, the prevalence of CYP2B6 516TT genotype was higher as compared to healthy individuals (35.3% vs. 30.5%, OR = 1.74). Patients with hepatotoxicity using tobacco had a higher prevalence of genotypes CYP2B6 516GT, 516TT, 516GT+TT as compared to healthy individuals (28.57% vs. 25.93%; 57.14% vs. 29.63%; 85.71% vs. 55.56%). Likewise, hepatotoxicity in patients consuming alcohol showed higher distributions of CYP2B6 516GT, 516TT, 516GT+TT genotypes (57% vs. 25.93%; 42.86% vs. 33.33%; 71.43% vs. 59.26%). Nevirapine users with hepatotoxicity overrepresented genotypes CYP2B6 TT and 516GT+TT as compared to efavirenz users (47.83% vs. 45.45%, OR = 6.88, 65.22% vs. 54.55%, OR = 1.56). Similarly, in nevirapine +alcohol users with hepatotoxicity, the frequency of CYP2B6 516GT, 516GT+TT genotypes was higher than with nevirapine +alcohol nonusers (40.0% vs. 11.11%, OR = 8.00, 80.0% vs. 27.78%, OR = 4.00). In HIV patients, nevirapine users had higher frequency of CYP2B6 516GT, 516GT+TT genotypes as compared to efavirenz users (42.02% vs. 25.00%, OR = 2.53; 72.27% vs. 58.33%, OR = 1.86). Likewise, in HIV patients, genotypes CYP2B6 516GT, 516GT+TT were predominant with nevirapine +alcohol users as compared to nevirapine +alcohol nonusers (57.89% vs. 34.57%, OR = 2.46; 78.95% vs. 69.14%, OR = 1.67). In multivariate logistic regression, taking nevirapine had a protection for severity of ARV‐associated hepatotoxicity (OR = 0.23, p = 0.005).

Conclusions

No significant association was detected between CYP2B6 516G>T polymorphism and susceptibility to ARV‐associated hepatotoxicity.

Role of CYP2B6 pharmacogenomics in bupropion-mediated smoking cessation

WHAT IS KNOWN AND OBJECTIVE

Pharmacogenomics holds promise in smoking cessation because of its potential to shed light on the complexity of drug metabolism and improve treatments using therapeutic agents. The cytochrome P450 2B6 gene (CYP2B6) encodes CYP2B6 enzyme that has been found to mediate the hydroxylation of bupropion, a smoking cessation aid. CYP2B6 exhibits a range of polymorphic variants that alter the pharmacokinetics and pharmacodynamics of bupropion. Genetic variations in CYP2B6 may influence the risk of adverse effects or efficacy of treatment with bupropion. The objective of this review was to investigate the influence of pharmacogenomics on smoking cessation therapy.

METHODS

A thorough literature search was conducted on PubMed, SCOPUS and EMBASE using keywords related to bupropion, smoking cessation, pharmacogenomics and CYP2B6. Research and review articles, case reports and clinical and preclinical studies pertinent to the research topic were identified, evaluated and summarized. Cited articles within the above-mentioned sources also provided pertinent information.

RESULTS

There is strong literature evidence to prove that CYP2B6 polymorphisms affect pharmacokinetic and pharmacodynamic properties of bupropion, thus affecting the therapeutic outcome of smoking cessation therapy.

WHAT IS NEW AND CONCLUSIONS

Complete understanding of pharmacogenetic variation of bupropion pharmacokinetics and pharmacodynamics will be beneficial for designing safer and more personalized smoking cessation therapy with improved outcomes.

A Mechanism-Based Population Pharmacokinetic Analysis Assessing the Feasibility of Efavirenz Dose Reduction to 400 mg in Pregnant Women

BACKGROUND

Reducing the dose of efavirenz can improve safety, reduce costs, and increase access for patients with HIV infection. According to the World Health Organization, a similar dosing strategy for all patient populations is desirable for universal roll-out; however, it remains unknown whether the 400 mg daily dose is adequate during pregnancy.

METHODS

We developed a mechanistic population pharmacokinetic model using pooled data from women included in seven studies (1968 samples, 774 collected during pregnancy). Total and free efavirenz exposure (AUC24 and C12) were predicted for 400 (reduced) and 600 mg (standard) doses in both pregnant and non-pregnant women.

RESULTS

Using a 400 mg dose, the median efavirenz total AUC24 and C12 during the third trimester of pregnancy were 91 and 87% of values among non-pregnant women, respectively. Furthermore, the median free efavirenz C12 and AUC24 were predicted to increase during pregnancy by 11 and 15%, respectively.

CONCLUSIONS

It was predicted that reduced-dose efavirenz provides adequate exposure during pregnancy. These findings warrant prospective confirmation.

Neuropsychiatric manifestations among HIV-1 infected African patients receiving efavirenz-based cART with or without tuberculosis treatment containing rifampicin

Purpose

Efavirenz-based combination antiretroviral therapy (cART) is associated with neuropsychiatric adverse events. We investigated the time to onset, duration, clinical implications, impact of pharmacogenetic variations, and anti-tuberculosis co-treatment on efavirenz-associated neuropsychiatric manifestations.

Methods

Prospective cohort study of cART naïve HIV patients with or without tuberculosis (HIV-TB) co-infection treated with efavirenz-based cART. Rifampicin-based anti-tuberculosis therapy was initiated 4 weeks prior to efavirenz-based cART in HIV-TB patients. Data on demographic, clinical, laboratory, and a 29-item questionnaire on neuropsychiatric manifestations were collected for 16 weeks after cART initiation. Genotyping for CYP2B6, CYP3A5, SLCO1B1, and ABCB1 and quantification of efavirenz plasma concentration were done on the 4th and 16th week.

Results

Data from 458 patients (243 HIV-only and 215 HIV-TB) were analyzed. Overall incidence of neuropsychiatric manifestations was 57.6% being higher in HIV-only (66.7%) compared to HIV-TB patients (47.4%) (p < 0.01). HIV-only patients were more symptomatic, with proportionately higher grades of manifestations compared to HIV-TB patients. Median time to manifestations was 1 week after cART initiation in HIV-only and 6 weeks after anti-TB (i.e., 2 weeks after cART initiation) in HIV-TB patients. HIV-only patients had significantly higher efavirenz plasma concentrations at 4 weeks after cART compared to HIV-TB patients. No association of sex or genotype was seen in relation to neuropsychiatric manifestations. Risk for neuropsychiatric manifestations was three times more in HIV-only patients compared to HIV-TB (p < 0.01).

Conclusions

Incidence of neuropsychiatric manifestations during early initiation of efavirenz-based cART is high in Tanzanian HIV patients. Risk of neuropsychiatric manifestations is lower in HIV patients co-treated with rifampicin containing anti-TB compared to those treated with efavirenz-based cART only.

Electronic supplementary material

The online version of this article (10.1007/s00228-018-2499-0) contains supplementary material, which is available to authorized users.

Adverse Neuropsychiatric Events and Recreational Use of Efavirenz and Other HIV-1 Antiretroviral Drugs

Efavirenz is a highly effective HIV-1 antiretroviral; however, it is also frequently associated with neuropsychiatric adverse events (NPAE) that include abnormal dreams, sleep disturbances, nervousness, anxiety, depression, and dizziness. The incidence of NPAEs upon initiation of treatment with efavirenz-containing medications is high, exceeding 50% in most studies. Although the NPAEs tend to decrease after the first month in many patients, they persist for long periods of time in others. Efavirenz-based treatment is generally well-tolerated in children, although some experience persistent concentration problems, as well as sleep disturbances, psychotic reactions, and seizures. In an effort to link basic with clinical research, parameters associated with efavirenz brain exposure are discussed, and factors that increase efavirenz levels are explored in depth as they are expected to contribute to NPAE risk. These include the role of modifiable and nonmodifiable risk factors such as diet, weight, and drug-drug interactions and sex, age, and ethnicity/pharmacogenetics. In addition to NPAEs, this review explores what is known about antiretroviral (ARV) drugs being used for recreational purposes. Although multiple ARV drugs are covered, special attention is devoted to efavirenz given that the majority of reports of NPAEs and illicit use of ARV drugs concern efavirenz. The evolving molecular mechanistic basis of NPAEs and abuse of efavirenz point to a complex and polymodal receptor pharmacology. Animal studies to date primarily point to a serotonergic mechanism of action. Recently emerging associations between HIV-associated neurocognitive disorder and efavirenz use, and possible contributions of the mitochondrial-immune-inflammatory-redox cascade are explored in the context of the signaling mechanisms that appear to be involved.

Polymorphisms in cytochrome P450 are associated with extensive efavirenz pharmacokinetics and CNS toxicities in an HIV cohort in Botswana

Inter-individual variability in efavirenz (EFV) pharmacokinetics and dynamics are dominantly driven by the polymorphism in cytochrome P450 (CYP) isoenzyme 2B6 516G>T. We hypothesized that additional CYP polymorphisms mediate the relationship between CYP2B6 516G>T, EFV metabolism, and clinical events. We investigated 21 SNPs in 814 HIV-infected adults initiating EFV-based therapy in Botswana for population pharmacokinetics, CNS toxicities, and treatment outcomes. Two SNPs (rs28399499 and rs28399433) showed reduced apparent oral EFV clearance. Four SNPs (rs2279345, rs4803417, rs4802101, and rs61663607) showed extensive clearance. Composite CYP2B-mediated EFV metabolism was significantly associated with CNS toxicity (p=0.04), with extensive metabolizers reporting more and slow and very slow metabolizers reporting less toxicity after one month compared to intermediate metabolizers. Composite CYP2B6 metabolism was not associated with composite early treatment failure. In conclusion, our data suggest that CNS-related toxicities might not be solely the result of super-therapeutic parent EFV concentrations in HIV-infected individuals in patients of African ancestry.

CYP2B6 Haplotype Predicts Efavirenz Plasma Concentration in Black South African HIV-1-Infected Children: A Longitudinal Pediatric Pharmacogenomic Study

South Africa has the highest burden of the human immunodeficiency virus (HIV) infection globally. Efavirenz (EFV), a frequently used drug against HIV infection, displays a relationship between drug concentration and pharmacodynamics effects clinically. However, haplotype-based genetic variation in drug metabolism in a pediatric sample has been little considered in a longitudinal long-term context. CYP2B6 plays a key role in variation of EFV plasma concentration through altered drug metabolism. We report here on a prospective clinical pharmacogenomics/pharmacokinetic study of Bantu-speaking children, importantly, over a period of 24 months post-initiation of EFV-based treatment in South Africa. We characterized the HIV-1-infected children (n = 60) for the CYP2B6 c.516G>T, c.785A>G, c.983T>C, and c.1459C>T single nucleotide polymorphisms (SNPs). These SNPs were determined using polymerase chain reaction/restricted fragment length polymorphism and SNaPshot genotyping. Longitudinal mid-dose EFV plasma concentrations were determined by LC-MS/MS and association analyses with genotypes and haplotypes at 1, 3, and 24 months were performed. The CYP2B6 c.516T/T genotype showed significantly higher EFV plasma concentrations (p < 0.001) compared to non 516T-allele carriers at all three time points. The minor allele frequencies (MAF) for CYP2B6 c.516T, c.785G, c.983C, and c.1459T were 0.410, 0.408, 0.110, and 0.000 respectively. Haplotypes were constructed using CYP2B6 c.516G>T,-c.785A>G and c.983T>C. The haplotype T-G-T presented with significantly increased EFV plasma concentrations compared to the reference G-A-T haplotype at 1, 3, and 24 months (p = 0.009; p = 0.003; p = 0.001), suggesting that the T-G-T haplotype predisposes a risk of EFV plasma concentrations >4 μg/mL. The clinical implications of these pharmacogenomics observations for EFV toxicity and treatment resistance warrant further future research.

Application of Physiologically Based Pharmacokinetic (PBPK) Modeling Within a Bayesian Framework to Identify Poor Metabolizers of Efavirenz (PM), Using a Test Dose of Efavirenz

Poor metabolisers of CYP2B6 (PM) require a lower dose of efavirenz because of serious adverse reactions resulting from the higher plasma concentrations associated with a standard dose. Treatment discontinuation is a common consequence in patients experiencing these adverse reactions. Such patients benefit from appropriate dose reduction, where efficacy can be achieved without the serious adverse reactions. PMs are usually identified by genotyping. However, in countries with limited resources genotyping is unaffordable. Alternative cost-effective methods of identifying a PM will be highly beneficial. This study was designed to determine whether a plasma concentration corresponding to a 600 mg test dose of efavirenz can be used to identify a PM. A physiologically based pharmacokinetic (PBPK) model was used to simulate the concentration-time profiles of a 600 mg dose of efavirenz in extensive metabolizers (EM), intermediate metabolizers (IM), and PM of CYP2B6. Simulated concentration-time data were used in a Bayesian framework to determine the probability of identifying a PM, based on plasma concentrations of efavirenz at a specific collection time. Results indicated that there was a high likelihood of differentiating a PM from other phenotypes by using a 24 h plasma concentration. The probability of correctly identifying a PM phenotype was 0.82 (true positive), while the probability of not identifying any other phenotype as a PM (false positive) was 0.87. A plasma concentration >1,000 ng/mL at 24 h post-dose is likely to be from a PM. Further verification of these findings using clinical studies is recommended.

Genetic Polymorphisms Affecting the Pharmacokinetics of Antiretroviral Drugs

BACKGROUND

Antiretroviral treatment is highly effective in enhancing HIV-positive patients' survival and quality of life. Despite an increased tolerability in recent years, a substantial amount of patients experience side effects. Antiretrovirals' efficacy and tolerability have been associated with plasma concentrations and single nucleotide polymorphisms in selected genes involved in drug disposition.

OBJECTIVE

Our aim was to review the current knowledge in genetic polymorphisms affecting plasma, intracellular or compartmental concentrations of antiretrovirals.

METHODS

A search of the PubMed database was conducted to identify relevant articles, using the following terms: 'pharmacogenetics' or 'pharmacogenomics' or 'single nucleotide polymorphisms' or 'genetic/allelic variants' and 'pharmacokinetics' or 'concentrations' and 'HIV' or 'antiretroviral'. Abstracts from the main HIV conferences during 2015 and 2016 were also searched using the same keywords. Abstracts were manually checked and, if relevant, full papers were obtained. Only articles published in English were selected.

RESULTS

Several genetic polymorphisms in genes coding enzymes involved in drug metabolism (cytochrome P450 isoenzymes and uridine diphosphate glucuronosyltransferases) and transport (P-glycoprotein, anionic and cationic transporters, other transporters), as well as nuclear receptors (pregnane X receptor and the constitutive androstane receptor), have been associated with concentrations of antiretrovirals. The extent of such influence, the conflicting data, and the potential clinical relevance are discussed in the main section of this article.

CONCLUSION

Genetic polymorphisms may affect antiretroviral disposition, as well as both efficacy and toxicity. Despite a large amount of data, such precious knowledge has seldom been applied in patients. Studies on the clinical relevance and cost effectiveness of tailoring antiretroviral regimens to patients' genetic assets are lacking, but their importance may grow with the increasing age and complexity of persons living with HIV/AIDS.

Multiphenotype association study of patients randomized to initiate antiretroviral regimens in AIDS Clinical Trials Group protocol A5202

Supplemental Digital Content is available in the text.

Background

High-throughput approaches are increasingly being used to identify genetic associations across multiple phenotypes simultaneously. Here, we describe a pilot analysis that considered multiple on-treatment laboratory phenotypes from antiretroviral therapy-naive patients who were randomized to initiate antiretroviral regimens in a prospective clinical trial, AIDS Clinical Trials Group protocol A5202.

Participants and methods

From among 5 9545 294 polymorphisms imputed genome-wide, we analyzed 2544, including 2124 annotated in the PharmGKB, and 420 previously associated with traits in the GWAS Catalog. We derived 774 phenotypes on the basis of context from six variables: plasma atazanavir (ATV) pharmacokinetics, plasma efavirenz (EFV) pharmacokinetics, change in the CD4+ T-cell count, HIV-1 RNA suppression, fasting low-density lipoprotein-cholesterol, and fasting triglycerides. Permutation testing assessed the likelihood of associations being by chance alone. Pleiotropy was assessed for polymorphisms with the lowest P-values.

Results

This analysis included 1181 patients. At P less than 1.5×10⁻⁴, most associations were not by chance alone. Polymorphisms with the lowest P-values for EFV pharmacokinetics (CYPB26 rs3745274), low-density lipoprotein -cholesterol (APOE rs7412), and triglyceride (APOA5 rs651821) phenotypes had been associated previously with those traits in previous studies. The association between triglycerides and rs651821 was present with ATV-containing regimens, but not with EFV-containing regimens. Polymorphisms with the lowest P-values for ATV pharmacokinetics, CD4 T-cell count, and HIV-1 RNA phenotypes had not been reported previously to be associated with that trait.

Conclusion

Using data from a prospective HIV clinical trial, we identified expected genetic associations, potentially novel associations, and at least one context-dependent association. This study supports high-throughput strategies that simultaneously explore multiple phenotypes from clinical trials’ datasets for genetic associations.

Allele and Genotype Frequencies of Cytochrome P450 2B6 516G>T Single Nucleotide Polymorphism in HIV-Negative and HIV-Infected Adult Nigerian Populations

Polymorphisms in genes have been found in most enzymes involved in drug metabolism, especially in the cytochrome P450 (CYP) family with considerable ethnic differences in their frequencies. Single nucleotide polymorphisms (SNPs) are the major source of these genetic variations. CYP2B6 516G>T SNP found in both CYP2B6*6 and CYP2B6*9 alleles significantly reduces CYP2B6 protein expression and enzyme activity with important implications on the pharmacokinetics and pharmacodynamic outcomes of some clinically relevant drug substrates. This study determined the frequencies of CYP2B6 516G>T SNP in HIV-negative and HIV-infected adult Nigerian populations. Three hundred unrelated subjects (150 each of HIV-negative volunteers and HIV-infected patients) of different Nigerian ethnic groups residing in Ilorin and Ile-Ife and its environs, respectively, were recruited and genotyped for their CYP2B6 516G>T genetic status using real-time polymerase chain reaction. Differences in allele and genotype frequencies between both populations were tested using Pearson χ test. Minor allele frequency of 36.4% and genotype frequencies of 38.7% GG, 50.0% GT, 11.3% TT and a minor allele frequency of 37.0% and genotype frequencies of 42.0% GG, 42.0% GT, 16.0% TT were obtained for the HIV-negative volunteers and HIV-infected patients, respectively. χ test indicated a significant relationship between genotype frequencies in both populations (P < 0.001). The minor allele and genotype frequencies obtained in the 2 populations significantly differ and corroborate previous studies, which have reported CYP2B6 516G>T SNP in various other African populations.

Cytochrome 2B6 polymorphism and efavirenz-induced central nervous system symptoms : a substudy of the ANRS ALIZE trial

OBJECTIVES

Single nucleotide polymorphisms in the cytochrome P450 (CYP) 2B6 gene have been associated with high interindividual variation in efavirenz pharmacokinetics. However, clinical data on the relationship of CYP2B6 polymorphisms with the occurrence of efavirenz-induced central nervous system (CNS) symptoms are limited.

METHODS

We analysed four polymorphisms in the CYP2B6 (516 G>T), CYP3A5 (6986 A>G) and ATP-binding cassette, sub-family B, member 1 (ABCB1) (2677 G>T/A and 3435 C>T) genes in HIV-infected adults virologically suppressed on a protease inhibitor-based regimen who switched to a regimen containing emtricitabine, didanosine and efavirenz in the setting of the ANRS ALIZE trial. Kaplan-Meier methods and Cox regression analysis were used to investigate their association with efavirenz plasma levels and CNS events up to 48 months after switching.

RESULTS

In total, 191 patients with a median age of 41 years, who were 87% male and 85% Caucasian, were enrolled in the study. Variant allelic frequencies were 0.49, 0.93, 0.59 and 0.63 for CYP2B6 516, CYP3A5 392, ABCB1 2677 and ABCB1 3435, respectively. The median efavirenz plasma concentration (MEPC) was 2.2 mg/L [interquartile range (IQR) 1.7-2.8 mg/L] and was significantly higher in patients with the deficient CYP2B6 516T. Overall, 242 CNS events were reported in 104 individuals (54%). No correlation was found between MEPC and CNS events. The occurrence of a first CNS event was lower in patients with the CYP2B6 516 G/G genotype vs. CYP2B6 516 T genotypes [50% (IQR: 40-60%) vs. 66% (IQR: 56-75%), respectively; P = 0.02]. In an adjusted Cox regression model, there was a tendency towards a higher risk of a first CNS event among carriers of the variant CYP2B6 516 T allele (relative risk 1.4 [95% CI, 0.99-2.1]; P?=?.06), compared with noncarriers.

CONCLUSIONS

The deficient CYP2B6 516 T allele is associated with higher efavirenz plasma drug levels and more frequent CNS-related symptoms.

Pharmacogenetic Optimization of Smoking Cessation Treatment

Worldwide, approximately one billion people smoke cigarettes. Cigarette smoking persists in part because long-term smoking cessation rates are modest on existing treatments. Smoking cessation outcomes are influenced by genetic factors, including genetic variation in enzymes that metabolize nicotine and smoking cessation medications, as well as in receptor targets for nicotine and treatment medications. For example, smokers with genetically slow nicotine metabolism have higher cessation success on behavioural counseling and nicotine patches compared with smokers with genetically fast nicotine metabolism. In this review, we highlight new progress in our understanding of how genetic variation in the pharmacological targets of nicotine and smoking cessation medications could be used to tailor smoking cessation therapy, increase quit rates, and reduce tobacco-related harm.

Population Pharmacokinetic Modeling To Estimate the Contributions of Genetic and Nongenetic Factors to Efavirenz Disposition

Efavirenz pharmacokinetics is characterized by large between-subject variability, which determines both therapeutic response and adverse effects. Some of the variability in efavirenz pharmacokinetics has been attributed to genetic variability in cytochrome P450 genes that alter efavirenz metabolism, such as CYP2B6 and CYP2A6 While the effects of additional patient factors have been studied, such as sex, weight, and body mass index, the extent to which they contribute to variability in efavirenz exposure is inconsistently reported. The aim of this analysis was to develop a pharmacometric model to quantify the contribution of genetic and nongenetic factors to efavirenz pharmacokinetics. A population-based pharmacokinetic model was developed using 1,132 plasma efavirenz concentrations obtained from 73 HIV-seronegative volunteers administered a single oral dose of 600 mg efavirenz. A two-compartment structural model with absorption occurring by zero- and first-order processes described the data. Allometric scaling adequately described the relationship between fat-free mass and apparent oral clearance, as well as fat mass and apparent peripheral volume of distribution. Inclusion of fat-free mass and fat mass in the model mechanistically accounted for correlation between these disposition parameters and sex, weight, and body mass index. Apparent oral clearance of efavirenz was reduced by 25% and 51% in subjects predicted to have intermediate and slow CYP2B6 metabolizer status, respectively. The final pharmacokinetic model accounting for fat-free mass, fat mass, and CYP2B6 metabolizer status was consistent with known mechanisms of efavirenz disposition, efavirenz physiochemical properties, and pharmacokinetic theory. (This study has been registered at ClinicalTrials.gov under identifier NCT00668395.).

Might ART Adherence Estimates Be Improved by Combining Biomarker and Self-Report Data?

BACKGROUND

As we endeavour to examine rates of viral suppression in PLHIV, reliable data on ART adherence are needed to distinguish between the respective contributions of poor adherence and treatment failure on high viral load. Self-reported data are susceptible to response bias and although biomarker data on drug presence and concentration can provide a superior, alternative method of measurement, complications due to drug-drug interactions and genetic variations can cause some inaccuracies. We investigate the feasibility of combining both biomarker and self-report data to produce a potentially more accurate measure of ART adherence.

METHODS

Data were taken from a large general-population survey in the Manicaland province, Zimbabwe, conducted in 2009-2011. HIV-infected adults who had initiated ART (N = 560) provided self-report data on adherence and dried blood spot samples that were analysed for traces of ART medication. A new three-category measure of ART adherence was constructed, based on biomarker data but using self-report data to adjust for cases with abnormally low and high drug concentrations due to possible drug-drug interactions and genetic factors, and was assessed for plausibility using survey data on socio-demographic correlates.

RESULTS

94.3% (528/560) and 92.7% (519/560) of the sample reported faithful adherence to their medication and had traces of ART medication, respectively. The combined measure estimated good evidence of ART adherence at 69% and excellent evidence of adherence at 53%. The regression analysis results showed plausible patterns of ART adherence by socio-demographic status with men and younger participants being more likely to adhere poorly to medication, and higher socio-economic status individuals and those living in more urban locations being more likely to adhere well.

CONCLUSION

Biomarker and self-reported measures of adherence can be combined in a meaningful way to produce a potentially more accurate measure of ART adherence. Results indicate that ART adherence in Manicaland is at best 69%, which not only allows for considerable room for improvement but also suggests that the area may be falling short of the UNAIDS' 90% target regarding viral suppression. Increased efforts are needed to improve ART adherence particularly amongst the young male population in rural areas of east Zimbabwe.

Single Heteroatom Substitutions in the Efavirenz Oxazinone Ring Impact Metabolism by CYP2B6

Previously, we observed that the oxazinone ring is important for cytochrome P450 2B6 (CYP2B6) activity toward efavirenz ((4S)-6-chloro-4-(2-cyclopropylethynyl)-1,4-dihydro-4-(trifluoromethyl)-2H-3,1-benzoxazin-2-one), a CYP2B6 substrate used to treat HIV. To further understand the structural characteristics of efavirenz that render it a CYP2B6 substrate, we tested the importance of each heteroatom of the oxazinone ring. We assembled a panel of five analogues: 6-chloro-4-(2-cyclopropylethynyl)-1,4-dihydro-2-methyl-4-(trifluoromethyl)-2H-3,1-benzoxazine (1), (4S)-6-chloro-4-[(1E)-2-cyclopropylethenyl]-3,4-dihydro-4-(trifluoromethyl)-2(1H)-quinazolinone (2), (4S)-6-chloro-4-(2-cyclopropylethynyl)-3,4-dihydro-4-(trifluoromethyl)-2(1H)-quinazolinone (3), 6-chloro-4-(cyclopropylethynyl)-3,4-dihydro-4-(trifluoromethyl)-2(1H)-quinolinone (4), and 6-chloro-4-(cyclopropylethynyl)-4-(trifluoromethyl)-4H-benzo[d][1,3]dioxin-2-one (5). The metabolism of compounds 1-5 was investigated using human liver microsomes, individual P450s, and mass spectrometry or UV/Vis absorbance detection. Steady-state analysis of CYP2B6 metabolism of 1-5 showed K_M values ranging from 0.3- to 3.9-fold different from that observed for efavirenz (K_M : 3.6±1.7 μm). The lowest K_M values, approximating 1 μm, were observed for the metabolism of 1, whereas the greatest K_M value, 14±6.4 μm, was found for 4. Our work reveals that analogues with heteroatom changes in the oxazinone ring are still CYP2B6 substrates, although the changes in K_M suggest altered substrate binding.

Pharmacokinetic, Pharmacogenetic, and Other Factors Influencing CNS Penetration of Antiretrovirals

Neurological complications associated with the human immunodeficiency virus (HIV) are a matter of great concern. While antiretroviral (ARV) drugs are the cornerstone of HIV treatment and typically produce neurological benefit, some ARV drugs have limited CNS penetration while others have been associated with neurotoxicity. CNS penetration is a function of several factors including sieving role of blood-brain and blood-CSF barriers and activity of innate drug transporters. Other factors are related to pharmacokinetics and pharmacogenetics of the specific ARV agent or mediated by drug interactions, local inflammation, and blood flow. In this review, we provide an overview of the various factors influencing CNS penetration of ARV drugs with an emphasis on those commonly used in sub-Saharan Africa. We also summarize some key associations between ARV drug penetration, CNS efficacy, and neurotoxicity.

Efavirenz and Metabolites in Cerebrospinal Fluid: Relationship with CYP2B6 c.516G→T Genotype and Perturbed Blood-Brain Barrier Due to Tuberculous Meningitis

Efavirenz (EFZ) has been associated with neuropsychiatric side effects. Recently, the 8-hydroxy-EFZ (8OH-EFZ) metabolite has been shown to be a potent neurotoxin in vitro, inducing neuronal damage at concentrations of 3.3 ng/ml. EFZ induced similar neuronal damage at concentrations of 31.6 ng/ml. We investigated the effect of genotype and blood-brain barrier integrity on EFZ metabolite concentrations in cerebrospinal fluid (CSF). We measured CSF drug concentrations in subjects from two separate study populations: 47 subjects with tuberculous meningitis (TBM) coinfection in Vietnam receiving 800 mg EFZ with standard antituberculous treatment and 25 subjects from the PARTITION study in the United Kingdom without central nervous system infection receiving 600 mg EFZ. EFZ and metabolite concentrations in CSF and plasma were measured and compared with estimates of effectiveness and neurotoxicity from available published in vitro and in vivo data. The effect of the CYP2B6 c.516G→T genotype (GG genotype, fast EFV metabolizer status; GT genotype, intermediate EFV metabolizer status; TT genotype, slow EFV metabolizer status) was examined. The mean CSF concentrations of EFZ and 8OH-EFZ in the TBM group were 60.3 and 39.3 ng/ml, respectively, and those in the no-TBM group were 15.0 and 5.9 ng/ml, respectively. Plasma EFZ and 8OH-EFZ concentrations were similar between the two groups. CSF EFZ concentrations were above the in vitro toxic concentration in 76% of samples (GG genotype, 61%; GT genotype, 90%; TT genotype, 100%) in the TBM group and 13% of samples (GG genotype, 0%; GT genotype, 18%; TT genotype, 50%) in the no-TBM group. CSF 8OH-EFZ concentrations were above the in vitro toxic concentration in 98% of the TBM group and 87% of the no-TBM group; levels were independent of genotype but correlated with the CSF/plasma albumin ratio. Potentially neurotoxic concentrations of 8OH-EFZ are frequently observed in CSF independently of the CYP2B6 genotype, particularly in those with impaired blood-brain barrier integrity.

Gene-gene interactions between DRD3, MRP4 and CYP2B6 polymorphisms and its influence on the pharmacokinetic parameters of efavirenz in HIV infected patients

Genetic factors have a significant impact on the PK variability of EFV, much higher than other non-genetic factors, such as demography. In this work we have performed a comprehensive PG analysis of genes encoding the major metabolizing enzymes and transporters of EFV, establishing a clear relationship between the PK parameters and genetic factors, which explain 50% of the variability in EFV PK parameters. The most relevant associations for metabolizing enzymes were found in CYP2B6 (rs3745274), in agreement with previous studies. The influence of transporters on the kinetics of EFV was also proved with significant correlations between the PK parameters of EFV and MRP4 (rs1751034, rs2274407). Analysis of gene-gene interactions with CYP2B6 was particularly useful to reinforce the role of MRP4 and to reveal unknown associations, such as that of DRD3. However, the role of DRD3 cannot be a direct effect but an indirect one due to physical proximity of NAT and the DRD3 locus in the genome.

Effects of CYP2B6 and CYP1A2 Genetic Variation on Nevirapine Plasma Concentration and Pharmacodynamics as Measured by CD4 Cell Count in Zimbabwean HIV-Infected Patients

The extremely high prevalence of HIV/AIDS in sub-Saharan Africa and limitations of current antiretroviral medicines demand new tools to optimize therapy such as pharmacogenomics for person-to-person variations. African populations exhibit greater genetic diversity than other world populations, thus making it difficult to extrapolate findings from one population to another. Nevirapine, an antiretroviral medicine, displays large plasma concentration variability which adversely impacts therapeutic virological response. This study, therefore, aimed to identify sources of variability in nevirapine pharmacokinetics and pharmacodynamics, focusing on genetic variation in CYP2B6 and CYP1A2. Using a cross-sectional study design, 118 HIV-infected adult Zimbabwean patients on nevirapine-containing highly active antiretroviral therapy (HAART) were characterized for three key functional single nucleotide polymorphisms (SNPs), CYP2B6 c.516G>T (rs3745274), CYP2B6 c.983T>C (rs28399499), and CYP1A2 g.-163C>A (rs762551). We investigated whether genotypes at these loci were associated with nevirapine plasma concentration, a therapeutic biomarker, and CD4 cell count, a biomarker of disease progression. CYP2B6 and CYP1A2 were chosen as the candidate genes based on reports in literature, as well as their prominence in the metabolism of efavirenz, a drug in the same class with nevirapine. Nevirapine plasma concentration was determined using LC-MS/MS. The mean nevirapine concentration for CYP2B6 c.516T/T genotype differed significantly from that of 516G/G (p < 0.001) and 516G/T (p < 0.01) genotypes, respectively. There were also significant differences in mean nevirapine concentration between CYP2B6 c.983T > C genotypes (p = 0.04). Importantly, the CYP1A2 g.-163C>A SNP was significantly associated with the pharmacodynamics endpoint, the CD4 cell count (p = 0.012). Variant allele frequencies for the three SNPs observed in this Zimbabwean group were similar to other African population groups but different to observations among Caucasian and Asian populations. We conclude that CYP2B6 c.516G>T and CYP2B6 c.983T>C could be important sources of nevirapine pharmacokinetic variability that could be considered for dosage optimization, while CYP1A2 g.-163C>A seems to be associated with HIV disease progression. These inter- and intra-population pharmacokinetic and pharmacodynamics differences suggest that a single prescribed dosage may not be appropriate for the treatment of disease. Further research into a personalized nevirapine regimen is required.